On February 6th, 2000 Yahoo portal was shut down for 3
hours. Then retailer Buy.com Inc. (BUYX) was hit the next day, hours after
going public. By that evening, eBay (EBAY), Amazon.com (AMZN), and CNN (TWX)
had gone dark. And in the morning, the mayhem continued with online broker
E*Trade (EGRP) and others having traffic to their sites virtually choked off.
How a "denial of service" attack works
In a typical connection, the user sends a message asking the server to authenticate it. The server returns the authentication approval to the user. The user acknowledges this approval and then is allowed onto the server.
In a denial of service attack, the user sends several authentication requests to the server, filling it up. All requests have false return addresses, so the server can't find the user when it tries to send the authentication approval. The server waits, sometimes more than a minute, before closing the connection. When it does close the connection, the attacker sends a new batch of forged requests, and the process begins again--tying up the service indefinitely.
"Denial of service" attack
How to block a "denial of service" attack
One of the more common methods of blocking a "denial of service" attack is to set up a filter, or "sniffer," on a network before a stream of information reaches a site's Web servers. The filter can look for attacks by noticing patterns or identifiers contained in the information. If a pattern comes in frequently, the filter can be instructed to block messages containing that pattern, protecting the Web servers from having their lines tied up.